Ponds in peril 

Globally, freshwater species have declined by 84% in the last 45 years, and wetlands are disappearing three times faster than rainforests. Here in the UK, we’ve lost 75% of our ponds in the last 100 years. Now, more than ever, we need to understand freshwater ecosystems to prevent irreversible species loss at a catastrophic scale. By simply listening, researchers are beginning to discover a bizarre and mysterious underwater soundscape that will help conserve threatened freshwater habitats. 

You might be familiar with the beautiful songs of humpback whales in the ocean, or the frantic buzzing of insects in a tropical rainforest, but what about ponds? What do they sound like? Who inhabits them? Ponds are in fact bursting with life and underwater sound - it’s like a festival!

Members of the band

Lots of different sounds can be heard in a pond, such as methane bubbling up from the sediment and fish drumming with their swim bladders, but some of the most common sounds are produced, rather surprisingly, by aquatic plants. As pond weeds photosynthesize in the hot sun they release tiny oxygen bubbles through small pores in the leaf surface called stomata into the water producing strange buzzing, whirring, and popping sounds.

Water beetles and boatmen also make a lot of noise in ponds, they use their legs and other parts of their anatomy to produce sound in a similar way to crickets, by stridulating - in other words, rubbing two hard body parts together.

In fact, the pygmy water boatman (Micronecta scholtzi) is capable of producing the loudest sound in the animal kingdom when scaled to body length at 105 decibels by rubbing its genitals against its belly - that’s as loud as a motorbike! 

Identifying species-specific sounds

We’ve suspected for a long time that different species of aquatic insects produce different sounds because species identification books focus on sound producing anatomy to distinguish between species. If different species use different structures to produce sound, then surely the sounds they produce will be species-specific. However, we still know very little about the sounds different species in ponds produce. 

Researchers are currently working to describe the sounds in pond soundscapes, such as these aquatic insect and fish sounds.

By cataloguing the species-specific sounds of aquatic insects, fish, and plants, researchers will be able to assess the condition of freshwater habitats based on the presence or absence of certain species simply by listening. Some species are really fussy and will only live in pristine habitats with good water quality, whereas others are only found in degraded habitats. By identifying these indicator species and the sounds they produce, an assessment of habitat quality can be made without having to kill plants and animals to later identify them under a microscope.